Subject: Chemistry — Solid State
Question: Consider an ionic solid $MX$ with $NaCl$ structure.
Construct a new structure $(Z)$ whose unit cell is constructed from the
unit cell of $MX$ following the sequential instructions given below.
Neglect the charge balance.
\(i\) Remove all the anions $(X)$ except the central one
\(ii\) Replace all the face centered cations $(M)$ by anions $(X)$
\(iii\) Remove all the corner cations $(M)$
\(iv\) Replace the central anion $(X)$ with cation $(M)$
The vale of
$\left( \frac{number\ of\ anion}{number\ of\ catons} \right)$ in $Z$
is \_\_\_\_\_\_\_\_\_\_\_\_\_\_.
Answer: 3
Solution: As per given information cation form FCC lattice and anion
occpy all the octahedral void.
So $M^{+}$ $X^{-}$ & Formula MX
4 ion 4 ion
After step I 4 ion 1 ion
After step II 1 ion 4 ion
After step III 0 ion 4 ion
After step IV 1 ion 3 ion
So ratio of $\frac{No.\ of\ anion}{No.\ of\ cation} = \frac{3}{1}$